1. Field of the Invention
The present invention relates to an optical type three-dimensional measurement method and a three-dimensional measurement device for obtaining measurement data or data based on measurement data.
2. Description of the Related Art
Three-dimensional measurement devices of the non-contact type are used for data input to computer graphics (CG) systems and CAD systems, three-dimensional measurements, and robotic visual recognition because of their high-speed measurement capability compared to devices of the contact-type.
Active methods for projecting reference light such as the slit projection method (also known as the light-sectioning method), spatial pattern encoding method, and striped pattern projection method are generally used as the measuring methods in portable three-dimensional measurement devices. Some devices also use the passive type stereo view method. For example, the slit projection method uses a slit light having a beam cross-section in the form of a linear band as a reference light, and scans in line sequence by deflecting the beam in the slit width direction. The slit length direction is the main scan direction, and the width direction is the subscan direction. Part of an object is illuminated at a point in time during scanning, and a bright line curved in accordance with the shape of the illuminated part appears on the photoreceptive surface of the image sensing system. Accordingly, a group od three-dimensional data which identify the object shape or the distances to various positions on the object is obtained by periodically sampling the brightness of each pixel of the photoreceptive surface during the scan.
In three-dimensional measurement via an active triangulation method, only the shape within a range of an object illuminated by a reference light and projected on the photoreceptive surface can be measured. Shadow areas on the photoreceptive surface cannot be measured even when illuminated by reference light. That is, a so-called occlusion is disadvantageously generated. To suppress the generation of occlusion, the baseline length of triangulation (i.e., the length of the line connecting the starting point of the projection light and the point of the received light) may be reduced to bring the principal point of the received light near the starting point of the projection light. However, this reduces resolution in the measurement depth direction, i.e., the distance direction. Even in the case of stereo view methods, resolution is reduced if the distance between the image sensing positions of two locations, i.e., the baseline length, is shortened.
When the frontal shape of an object is long and narrow, and the depth dimension is small, the majority of the photoreceptive surface is a region which does not receive the projection of the object image, thereby greatly reducing the efficiency of the photoreceptive surface. It is desirable that the projected object image is larger than the photoreceptive surface from the perspectives of measurement accuracy and reduction of unnecessary data.